Metals possess many desirable properties that make them the material of choice for a variety of applications. But metals are often quite dense and, in applications in which “weight” is of particular concern, it might not be feasible to use metal as fabrication material.
Due to a weight advantage relative to metal, fiber-reinforced composite materials, such as fiberglass, etc., are sometimes used as structural materials for weight-critical applications. But this weight benefit comes at a price; hardware fabricated from composite materials often does not provide the durability (e.g., wear resistance, temperature resistance, etc.) of metal hardware.
Launch-system hardware, such as a launch tube, is an example of an application that requires the performance/durability of a metal but would benefit from the weight advantages of a composite. In fact, metal has historically been used as the construction-material-of-choice for launch tubes. The weight reduction offered by a composite would be desirable, but it might be problematic for a composite launch tube to withstand the physical wear caused by launch of a projectile or the extreme temperatures and erosive character of missile exhaust.